Methods for using inert gas



Aug. 13, 1963 R. A. PLUMMER ETAL 3&9

METHODS FOR USING INERT @As Filed Feb. 6, 1961 3 Sheets-Sheet l Allg- 13, 1963 El. A. PLUMMER ETAL 3,3@9528 METHODS FOR USING INERT GAS Filed Feb. 6, 1961 I5 Sheets-Sheet 2 Aug. 13, E963 R. A. HUMMER ETAL 3&00523 METHODS FOR USING INERT GAS 3 Sheets-Sheet 3 Filed Feb. 6, 1961 aired Texas Filed Feb. 6, 1961, Ser. No. 87,291 16 Claims. (Cl. 166-ft2) This invention pertains to methods for using an inert gas, such as, for example, nitrogen, in underground oil or gas well operations. Among the uses for which an inert gas such as nitrogen may be employed according to the invention in underground oil or gas well operations are for acidizing, paran solventing, surfactant, detergent, corrosion inhibition, and fracturing treatments. In each case, a suitable agent or reactant is introduced in the form of an aerated fluid, the agent being atomized or broken up by introduction thereof into a high-pressure gas stream of the inert gas.

A principal object of the invention is to provide methods for introducing reactive materials into an oil or gas well.

Another object of the invention is to provide such methods whereby the reactant may be removed from the well easily after use.

Another object of the invention is to provide such methods whereby a high-pressure inert gas, such as nitrogen or carbon dioxide, or the like, is used as the carrier for the agent, whereby down-the-hole back pressures in the well can be overcome by the head imposed by the introduced gas and agent carried thereby.

Another object is to provide such methods taking due adventage of the solubility characteristics of the gas.

Brietiy, the invention includes use of an inert gas such as nitrogen to introduce acidizing, parailin solventing, surfactant and detergent, corrosion inhibition, and the like, and fracturing agents, into wells at high pressures and then, in most cases, removing the agent before the well is brought in. This is all accomplished by aerating the liquid reagent in use to bring same into intimate contact with the well formation into which it is introduced, the pressured gas used as the aerating agent causing return of the agent from the well after it is spent or after its use is completed.

Other objects and advantages will appear from the following detailed description of the invention, reference being made to the accompanying drawings, of which:

FIGURE l is a vertical crosssectiona1 view of a well and apparatus used in conjunction therewith, the drawing being partially in schematic representation form; and,

FIGURES 2 and 3 are vertical cross-sectional views in schematic representation, showing apparatus similarly as FIGURE 1 in modified conditions.

Referring to the drawings in detail, and first primarily to FIGURE l, there is shown a well l having a casing string 11, a tubing string 12, and a casing head 13. The equipment of the well is subject to wide variation, as is known in the art, and this invention is not limited to cases wherein the exact equipment herein described is employed. Also shown is a tubing head 14 surmounting casing head 13, a master valve 15 surmounting the adapter and having-lateral outlet 16, and an upper manifold titting 17.

A tank truck or like apparatus indicated generally by reference numeral 18 has an insulated tank 19 in which a supply of liquid nitrogen is maintained under low temperature conditions and at approximately atmospheric pressure. Other inert gas may replace the nitrogen, which is used by way of example only. Associated with tank 19 is a pump 21 and a heater 22 which is usually of the gasolinetired type for etliciency of operation and 3,1%,523 Patented ug. 13, 1963 ilse for simplicity in use. The pump and heater apparatus, together with the apparatus of truck 18, are here incompletely shown, being more completely shown in our copending application S.N. 85,288, filed January 27, 1961, and entitled, Method and Apparatus for Transportation and Delivery of inert Gas." The details of the apparatus and the method ot' its use will not be completely explained here, but reference to said other application may be had for details of the apparatus and methods, as shown therein.

Casing 11, as shown in the drawings, is shown as a schematic representation, it being well known that a plurality of casings are usually provided in wells and these being concentrically disposed to different depths below the earth's surface 25. However, for the purposes of this application, a showing of a single casing 11 is suicient although plural casing arrangements of various types may be employed and in some cases the .s0-called tubingless completion technique may be employed where there is no casing at all in the well hole and instead the earth surrounding the well is in direct contact with one or more tubings (called casings) to provide production from the well.

The apparatus of truck 18 is adapted to supply gaseous nitrogen at elevated pressures of up to 10,000 p.s.i.g. or higher as determined by the exact character of apparatus provided. At any rate, high-pressure nitrogen gas of higher pressure than normally provided in connection with well operations is supplied by the apparatus of truck 18.

Tubing 12, as shown in the drawings, extends down nearly to the lower end of casing 11, the lower end of casing 11 being designated by reference numeral 26. Tubing 12 will, for example extend to a slightly higher elevation indicated by reference numeral 27 at its lower end. A well formation 28 is pierced by well 10. It is upon formation 28 that reactions with different agents are to be accomplished. The lower end of casing l1 is cemented, as is customary in the art, by a cement formation 29. Plural perforations 30 are disposed through the cement 29 and through the wall of casing 11 so that for-` mation 28 can be reached from the interior of the casing or from the interior of tubing 12 through its lower end 27.

In carrying out the method herein disclosed in any of its forms, the first step is usually the introduction of pressured gas into the formation to provide a gas cushion in the formation and in the casing or tubing. The gas cushion may be omitted. For purposes of illustrating the invention, let use assume that casing 11 is filled with an inert well fluid, for example, drilling mud, at the 0utset, drilling mud being a weighted or high-gravity fluid capable of holding back well pressures from the surface of the well. -In other words, the weight of the mud counterbalanccs the pressure at the lower end of the well; i.e., the formation pressure.

ln FIGURE l of the drawings, there is shown no packer device in the annulus between casing 1l and tubing 12, while in FIGURES 2 and 3 such packer is provided. Under the conditions of FIGURE l, with no packer, it is possible to inject gas into the well with the mud in place and with the gas pressure acting against the lower end of the mud column to support same, and with the mud acting as a gas seal in the annulus.

However, better practice when no packer is provided is to circulate the mud out of the casingdurbing annulus by gas displacement, and then to either continue injection of the `gas for carrying out the treatment, e.g. to form the pressured gas cushion, etc., or, on the other hand, to inject un-aerated liquid reactant into 4both tubing and casing `to allow the liquid to fall to the bottom of the well. By this latter alternative procedure, the falling liquid will be come sufficiently aeratcd so that after a suilicient amount thereof has been put at the bottom of the well, the process may be continued thereafter according to the principles set forth herein, commencing after reactant introduction into the well. Any other suitable means for closing the annulus may be employed.

With the annulus `between casing and tubing either' filled with pressured gas, as in FIGURE l, or closed off with a packer device 33, as in FIGURES 2 and 3, pressured gas introduction is continued, with the gas being forced laterally outward from the well into the formation, to force the formation fluids 32 farther and farther from the well.

In pipe 34, connecting heater 22 with the well head, there is provided a jet or nozzle arrangcment into which leads a lateral pipe 36, pipe 36 being used for introduction of a reactant into the gas stream. After sufficient gas cushion has been put into place in the well .to properly condition the well for treatment, a reactant such as an acid for acidizing treatment of the well, or a surfactant or detergent for cleansing or other surface action of the materialsgin the well, or a corrosion inhibitor for inhibition of corrosion of well equipment such as tubing l2 or casing 1l or some other apparatus disposed in the well, or ya fracturing agent which usually consists of suspended particles in a liquid carrier for opening up the formation, or a solvent for dissolving some objectionable material such as, for example, paraffin from the casing, tubing, or

well may 'be introd-uced following the gas cushion. High pressure nitrogen or other inert gas is delivered rfrom truck i8 through lpipeline 34 and nozzle 35 and the reactant is introduced into the gas stream through pipe 3d. The resulting mixture of gas and reagent is in the form of a froth or gasied liquid wherein a large amount of gas in small-bubble form is present in the liquid being carried. There is always some gas in solution in the liquid. The concentration of the reagent-gas mix-ture is expressed commonly in the form of a solution ratio, the term solution-ratio `being the ratio of standard cubic feet of gas to LlZ-gallon barrels of reactant in liquid form. The solution ratio may be anything from to 4,000 standard cubic feet per barrel, the Vmost commonly-used ratios being in the range of from about 200 to about 600 standard cubic feet of gas per 42-gallon barrel of liquid reactant. Solution ratios above 4,000 will in most cases be substantially unusable. vThe high pressure of the gas-liquid solution maintains it in the dispersed form so that there is no substantial separation of gas from liquid during use n thereof.

Following the gas cushion designated yby reference numeral 37 and referring now particularly to FIGURE 2, the reactant is introduced into thewell to spread from the casing 11 in the well to a predetermined, desired distance into the formation. Gas cushion 37 is pushed farther into the formation ahead of the reactant froth or aerated mixture. The reactant mixture is indicated by reference numeral 38 in the drawings. An optimum rate of introduction of fluids into the well may -be determined in order to prevent by-passing or channeling of whatever is then -being introduced into the well. lf introduction at too slow a rate is used, then the time factor which is costly s added to the cost of the well, whereas when too fast an introduction is used, channeling or bypassing occursand ineffective treatment results. However, the aerated liquids resist channeling to a large degree, so that the rate of introduction into the formation is not as critical as it is in the case of unaerated liquids.

As more and more reagent-gas mixture is introduced into the well formation through tubing l2, the gas cushion spreads farther and farther into the formation until ultimately enough reagent mixture has been introduced. Thereafter, an additional vamount of pressured gas is introduced behind the reagent to purge the tubing of the reagent in case the reagent is reactive with the tubing on long contact, or to remove the reagent to areas farther from the well for treatment of the formation at those points. The second gas cushion, indicated by reference numeral 32 in the drawings, may in some cases be su'bstituted or followed by liquid-displacing agents, for example light oil, salt water, fresh water, or any other material deemed suitable to follow the treatment as a displacement agent, the nature of the agent having little or no effect on the treatment, and gas probably 4being the most efhcient displacing agent to use. Therefore, the gasiiied reagent may be displaced to areas further into the formation from the well bore by the introduction of a displacing fluid into the well following the gasified reagent, and the displacing fluid may be one of the agents named above or may be pressured nitrogen or other inert gas of the type described.

The reagent employed, whether it be an acid, a surfactant, an inhibitor, a fracturing agent, a solvent, or a detergent, `will `be retained in contact with the formation as described for a period of time either for the reagent to become dissipated or spent duc to complete reaction with the formation materials, or until the treatment has had suflicien-t time for completion. ln the case of solvents, for example, when solution of whatever is to be dissolved from the well, for example paraffin, is complete, then no further treatment is necessary and it is time to properly stop the treatment by withdrawal of the treating agent.

Removal or withdrawal of a treating agent mixture from the well is accomplished as follows (see FIGURE 3, particularly): The interior of tubing l2 is open for flow through a side-arm choke device 40, flow to the choke from the well head being controlled by the valve 41. Upon opening of valve 41, and closing of control valve d2 in pipe 315i, a controlled rate of llow of the displacement agents, Whether it be gas or liquid, is achieved through the choke. This causes gradual reduction of pressure at the lower end of the well as the displacement agent is allowed to flow out of the well, and eventually the aerated reactant mixture passes up through tubing 12 and out of the choke. The high-pressure gas cushion is operative in causing this removal of a reagent from the well, although the same removal may be accomplished less eciently if the gas cushion is omitted and the reactant passed into the well first. Since the gas cushion and reactant mixture and displacement agent have all been 'held at a pressure higher than the gas-introduction pressure which may be as high las 10,000 p.s.i.g. or higher, the bottomhole pressure may be as high as 15,000 or 20,000 p.s.i.g. This high pressure causes substantially all of the spent or used reactant to be purged from the well, since enough of gas cushion 37 was lirst introduced to result in this substantially complete purging of the reactant.

After the gas cushion has flowed up through the interior of tubing l2 out through the choke device 40, the Well will usually come in, that is, production from the well will commence. The production of liquid petroleum or petroleum gas from the well finally purging the well of the inert gas, for example, nitrogen, so that the well is free of introduced materials yand production can continue in a normal fashion thereafter.

The above description of the introduction, treatment, and removal of the treating medium will bc applicable to any of the treatments therein mentioned, which will now oe explained individually in further detail.

Une treatment for which the method herein disclosed may be effectively employed is the acidizing treatment of a well to either change the condition or form of materials comprising the formation, or to remove objectionable salts and the like present in the formation. Among acids which may be used for acid treatment of well formations are the acid known commonly as muriatic or hydrochloric acid, sulphuric acid, nitric acid, sulfonic acids, fluorinecontaining acids such as hydroiluoric acid, and others. These acids are useful in breaking down certain formation materials, in cleaning certain gummy materials from w'lls, in adjusting the pH characteristics of the formation materials to change their water-holding capacities, and for other reasons. The acids react with the formation mav terials usually resulting in reaction products including a gas plus water. The gas may be either a component of the original acid or a resultant gas, such as carbon dioxide, resulting from reaction with the formation material. In lany case, the reaction products are dispersed substantially in the treating medium so that they are removed from the well therewith at a later time. This is somewhat different from treatments with liquid acids wherein the gases resulting from reaction or break-down on the acid are not particularly soluble in many cases and pockets thereof may be formed in the formation around the well. However, use of a gas as a cushioning agent and for later removal of the reagent from the well provides for ybetter removal of the reaction gases and the water produced by the reaction. The acrated or foam-like Characteristics of la reactant mixture tends to take into solution either liquids or gases produced during the treatment so that they are efficiently removed.

Another treatment for -which the methods 'herein disclosed maybe employed is in solvent treatment of oil or gas wells. Solid materials such as paraffin frequently Abuild up around the well and in the casings and tubings extending into the well. The solids may be introduced according to the methods herein disclosed only to encompass the casing 4and tubing or may be further dispersed into contact with the formation for the treatment, depending upon where the condition requiring solvent treatlment exists in the well. After the solvent suitable for dissolving the blocking material has been in contact for a sufficient length of time to dissolve same, the solvent in aeratcd form with the inert gas, such as nitrogen, is removed from the well by the pressure of the reaction mixture and the gas cushion, as Ihas already been described.

Another treatment for which the method is useful is the treatment employing surfactants and/or detergents. These are used to dissolve certain materials which may be present in the well and to wash and clean cakes of mud such as bentonite clays from the well, from well screens present at the bottom of the well, and from any other apparatus which may `be in place in the well. Detergents and surfactants are useful in breaking down hydrated materials such as bentonite in particular, the detergent causing a change in water-combining properties of the bentonite to free the bentonite into particular form for removal with the treating aerated solution.

For corrosion-inhibitor treatment of the well, for eX- ample by long-chain amines, the amine solution is dispersed with gas, as heretofore described, at nozzle 3S so that the mixture when pressure-introduced into the welt is in intimate contact with all equipment in the well. After a suflicient time for action of the corrosion inhibitor has been allowed, the corrosion-inhibitor solution is removed as heretofore described.

For fracturing of the well formation, the inert gasfracturing liquid acrated solution is introduced as heretofore described. The fracturing solution will usually be of solid particles dispersed in a liquid carrier. The liquid may be water, light oil, or other carrier medium. The gas pressure forces the particles, for example, sand, into the small openings of the formation which are opened up as a result of the gas pressure to allow passage of the particles thereinto. The particles become wedged in the cracks and crevices and minute openings of the form-ation so that when the displacing medium, the reaction carrier, and the gas cushion are removed in the heretofore described manner, the particles will remain in 'the formation to keep the formationfpores and openings lin open condition more or less permanently. This results in increased flow of oil and gas from the formation once the well is brought in.

The solubility characteristics of the gas are utilized to advantage to obtain -thc maximum benefits of each of thc treatments according to this invention, and par ticularly when the inert gas employed is nitrogen. Nitrogen, at thc conditions contemplated, is less soluble in the liquid, whereas carbon dioxide, air, and most other gases are more soluble in the liquid the higher the pressure.

When nitrogen is used, for any of the described treatments, the nitrogen-acrilied reactant liquid contains nitrogen in solution, in an amount dependent on the pressure and temperature. When the aerified liquid reaches the bottom of the well, there is a pressure drop across the casing, or the like, separating the well interior from the formation, so that the pressure is greater in the well than in the formation. Therefore, as the acrated liquid ows from the well to the formation, the amount of nitrogen in solution (as distinct from the bubble state) decreases. However, since the well temperature is greater than the temperature of the acrated liquid, the temperature of the aerated liquid increases approaching the well temperature. lf Ithe acrated liquid temperature is below 200 F., the solubility of ith 'i n decreases and gas originally in the solution Ibreaks out. As the temperature of the Iaerated'liquid rises above 200 F., the solubility nitrogen increases thereby increasing the amount of gas going into solution. Later, after the pressure in the formation has been increased due to further gas introduction thereinto, there is more nitrogen in solution. This solubility change can be used to advantage.

While the later portion of the aeriied reactant is being forced into the formation, and while the pressured second gas cushion is being introduced, the formation pressure increases. This causes nitrogen to go into solution, and causes increased penetration of 'the aerified liquid into the small openings of the formation. Therefore, increased Contact of the reactant with the formation is obtained, nitrogen coming in and going out of solution within fthe formation being very effective in this regard since lthe bubble size is minu-te.

After the action of the reactant is complete, the formation pressure decreases during withdrawal of the aeried reactant. This results in continuous expansion of nitrogen, causing more effectual withdrawal of the gas phase of the mixture.

Mixtures of nitrogen with inert gases of opposite solubility properties results in the exact aerilied liquid characteristics and performance desired.

In case of fracturing, the sand or other formationopening solid is more effectively dispersed in the formation when nitrogen is used, because of the described supen'or penetration and opening up of the small openings of the formation.

Squeeze treatment of formations is possible according to the invention, the high gas pressures employed and the high pressures resulting at the bot-tom of the well being adaptable for squeezing or forcing almost any material desired into the formation.

Sometimes it will be desirable to not remove the reaction material from the formation after treatment. To accomplish this result, the gas cushion 37 will usually be omitted, 4and aerification of the reactant liquid may also be omitted. Elimination of gas cushion 37 results in less flow of gas from the well at the time that the choke 40 How is commenced, so that the reaction material will remain behind in the formation in substantial amount. Some of the reaction material will, of course, be carried out of the well by the production following the treatment, but a residual amount may retain for a long period of time so that conditions in the well are affected thereby more or less permanently.

It has already been mentioned Ithat the equipment shown in the well lltl is not a controlling factor for the methods herein disclosed. In FIGURE 3 of the drawings, there is shown a packer and circulating sleeve apparatus 50 in the well above the formation level. By a proper manipulation of the circulating vsleeve flow controis, aerated reactants such as corrosion inhibitors and paraffin solvents may be introduced into the casing annulus above the packer.

The invention herein disclosed is of broad application. The introduction of high-pressure inert gases into wells has not heretofore been accomplished. It is lcnown to f introduce gases such as natural gas (methane), and the like, into wells, these commonly being present in highpressure zones so that they may be introduced at sufficiently high pressures. It has not been known to have available high-pressure linert gas such as nitrogen, which is not explosive and which is not corrosive, and which may be 'transported to the well site for use in etcient and simple manner. The feature of removing the reactive material from the Well -by virtue of a high-pressure cushion rst introduced into the well ahead of the reacting material is not known in the art prior to this application.

There are many advantages in using an inert gas such as nitrogen, etc., instead of air for the processes disclosed herein. Air results in inflammable and explosive mixtures with petroleum materials. Air aggrevatcs corrosive conditions. High-pressure compressors must be used to make air available at the well site at the pressures required. Nitrogen and the other inert gases contemplated do not have these harmful characteristics. Further, the inert rgases do not react chemically with the formation fluids to cause dangerous or harmful conditions in the wells. Air, having inverse solubility characteristics as compared with nitrogen, is not capable of the increased formation penetration necessary particularly in connection with fracturing of well formations.

While preferred methods according to the invention have been shown and described herein and many modifications thereto may be made by persons skilled in the art without departing from the spirit of the invention, and it is intended to protect by Letters Patent all forms of the invention falling within the scope of the following claims.

What is claimed is:

l. Method for performing well operations, comprising at the well site, pumping a stream of liquited inert gas to increase its pressure, heating the pumped liquied gas to vaporize the gas to form high pressure inert gas, gasifying a reagent in liquid form with said high. pressure inert gas prepared at the well site, passing the gasitied reagent into the well under pressure to contact desired dass 8 portions of the well and formations through which the well extends therewith, maintaining said contact under said pressure for a desired period of time, and venting said pressure to cause return of spent gasifted reagent from the well.

2. Method according to claim 1, said reagent comprising at least one acidic material.

3. Method according to claim 1, said reagent comprising at least one solvent material.

4. Method according to claim l, said reagent comprising at least one detergent material.

5. Method according to claim 1, said reagent comprising a fracturing iluid.

6. Method according to claim l, said reagent comprising at least one corrosion inhibiting material. v

7. Method according to claim l, said inert gas being nitrogen.

8. Method according to claim l, including passing a quantity of said pressured inert gas into the well before passing said gasified reagent into the well, said gas providing a cushion in the well and assisting in return of spent gasitled reagent from the Well.

9. Method according to claim 8, said reagent comprising at least one acidic material.

10. Method according to claim 8, prising at least one solvent material.

1l. Method according to claim 8, prising at least one detergent material.

12. Method according to claim 8, prising a fracturing uid.

13. Method according to claim 8, said reagent comprising at least one corrosion inhibiting material.

14. Method according to claim 8, said inert gas being nitrogen.

15. Method according to claim 1, including passing said high pressure inert gas prepared at the well site into the well following said gasified reagent `to displace said gasified reagent farther into the formation.

16. Method according to claim 15, said liquied inert gas being liquid nitrogen.

said reagent comsaid reagent cornsaid reagent comlllefetences Cited; in the file of this patent UNITED STATES PATENTS 2,053,285 Grebe Sept. 8, 1936 2,850,098 Moll etal Sept. 2, 1958 42,964,109 Martin Dec. 13, 1960 l 3,004,594 Crawford Oct. 17, 1961 3,063,499 Allen Nov. 13, 1962 

1. METHOD FOR PERFORMING WELL OPERATIONS, COMPRISING AT THE WELL SITE, PUMPING A STREAM OF LIQUID INERT GAS TO INCREASE ITS PRESSURE, HEATING THE PUMPED LIQUIFIED GAS TO VAPORIZE THE GAS TO FORM HIGH PRESSURE INERT GAS, GASIFYING A REAGENT IN LIQUID FORM WITH SAID HIGH PRESSURE INERT GAS PREPARED AT THE WELL SITE, PASSING THE GASIFIED REAGENT INTO THE WELL UNDER PRESSURE TO CONTACT DESIRED PORTIONS OF THE WELL AND FORMATIONS THROUGH WHICH THE 